A known rotation angle detection device is disclosed in JP2001-317909A. The rotation angle detection device disclosed includes a housing equipped with a Hall IC (magnetic sensor), a rotation shaft (shaft member) operated so as to rotate as a unit with an operated member, and a rotor core (rotation member) having a magnet. When the rotor core rotates along with a rotation of the operated member such as a throttle valve, in response to a rotation angle of the rotor core, a magnetic flux density passing through the Hall IC varies. Then, in response to this magnetic flux density, an output of the Hall IC varies. A control circuit reads this output of the Hall IC and then detects a rotation angle of the rotor core and the operated member.
However, according to the aforementioned rotation angle detection device, the rotor core and the rotation shaft are integrally fixed to each other by means of riveting, and the like. That is, the rotor core and the rotation shaft are not rotatable relative to each other and are connected in such a manner that axes of the rotor core and the rotation shaft are not tiltable to each other. When a stress involving a tilting component, i.e. a stress that causes the axis of the rotation shaft to tilt relative to a fixed axis of the housing, is added to the rotation shaft via the operated member, a position of the magnet provided at the rotor core relative to the Hall IC provided at the housing is changed, thereby decreasing rotation angle detecting accuracy.
Thus, a need exists for a rotation angle detection device of which rotation angle detecting accuracy is prevented from decreasing even if a stress involving a tilt component is applied to a shaft member via an operated member.